1. Field of the Invention
The present invention relates to an apparatus for the self-dosing of a liquid medicine and also to a system in which the apparatus is incorporated. More particularly, the present invention relates to an apparatus which may be incorporated in a system or used as an independent device so as to be operated by a patient for the purpose of repeatedly dosing small amounts of, for example, analgesics to relieve postoperative pain or small amounts of an anticancer medicine to relieve cancer pain, or one-shot dosing of other medicines.
2. Description of the Related Art
It is becoming popular in anesthetic treatment to repeat or continue the administration of small amounts of an analgesic for the control of postoperative or cancer pain, wherein a certain device is used and an epidural catheter is inserted into a patient's body. On the other hand, the conditions of patients vary, and some patients may suffer acute pain during the continuous administration of prescribed amounts of analgesics. Therefore, there have been proposed various kinds of apparatuses adapted for use by a patient himself or herself in the event of such acute pain. These apparatuses are designed to allow the patient to make a one-shot administration of an analgesic, as disclosed for example in Domestic Republishing Gazette Sho. 63-501195 of an International Patent Application.
This apparatus for the patient-controlled delivery of a beneficial agent comprises, as shown in FIG. 5(a) of the present application, a chamber 90 defined between a raised plateau 98 of a back plate 86 and a circular flexible sheet 96. The chamber 90 is connected to conduits, which are respectively attached to and communicate with a bladder or container of the agent and to a catheter or other medical device. The flexible sheet 96 supports a floating plate 100 disposed thereon. A button-like control switch 84 is located above the floating plate so as to be pushed thereto by the patient. A base portion of the control switch 84 is journaled on the back plate by a pivot pin 116, and a coil spring 124 surrounds this pin. When the switch 86 is pushed by the patient, the chamber 90 will be compressed as shown in FIGS. 5(b) and 5(c) so that the beneficial agent is supplied to him or her via one of the conduits. Upon retraction of the patient's finger from the button-like switch 84, the coil spring 124 causes it to return to its home position shown in FIG. 5(d).
It is noted here that the flexible sheet 96 in the prior art apparatus remains pressed as illustrated in FIG. 5(d), even after the patient has removed his or her finger from the switch 84. Thus, the refilling of the chamber 90 with the beneficial agent is done only by a moderate compressive force imparted by the bladder to the beneficial agent therein. The elastomeric bladder is, however, of such a nature that only small amounts of the agent can be dosed. Consequently, the beneficial agent is fed to the chamber at a slow speed (see Gazette 63-501195, page 6, lines 13-19).
This feature of the prior art apparatus is disadvantageous in that prompt and rapid refilling of the agent for the next dose is not possible.
Further, the patient cannot change or adjust the quantity of one dose, because only a limited volume of the agent can be discharged at a time by means of the conventional apparatus. Such a limited quantity and a slow refilling render it impossible for the patient to dose himself or herself a freely selected quantity of the agent at any desired rate.
It is also noted that, as can be seen in FIGS. 5(a) to 5(d), this conventional apparatus is of a comparatively complicated structure which can be manufactured only at a relatively high cost. In addition, the liquid agent is likely to leak from the periphery of the flexible sheet 96.